The present invention relates to a recording sheet conveyance apparatus used for an image forming apparatus such as an electrophotographic copier and laser printer, and more particularly relates to improvements in a recording sheet conveyance apparatus used for an image forming apparatus which can record an image on both sides of a recording sheet.
In an image recording apparatus such as an electrophotographic copier and laser printer, various techniques of an automatic two-sided recording apparatus by which not only one-sided recording but also two-sided recording can be carried out, have been proposed. In an automatic two-sided recording apparatus of the prior art, an image is formed on one side of a recording sheet in an image forming section, then the recording sheet is once stocked in an intermediate section, and after that, the recording sheet is conveyed again to the image forming section so that an image can be formed on the other side of the recording sheet. The aforementioned automatic recording sheet circulating apparatus is disclosed in Japanese Patent Application Open to Public Inspection Nos. 82247/1984, and 114227/1984.
In the case of a two-sided copy mode for a single recording sheet, after an image has been recorded on one side of the recording sheet, the recording sheet is discharged outside of the apparatus by a discharging roller and reversed, and then the recording sheet is supplied to the image forming section again so that an image is formed on the opposite side to the recorded side of the recording sheet.
In the case of a two-sided copy mode for a plurality of recording sheets, recording sheets on which an image has been transferred and fixed, are supplied again to the image forming section so that an image is formed on the opposite side.
The aforementioned conventional two-sided copier in which one sheet and a plurality of sheets of recording sheets are circulated and conveyed, is disclosed in Japanese Patent Application Open to Public inspection Nos. 111955/1983 and 183471/1987.
According to Japanese Patent Application Open to Public Inspection No. 111955/1983, in order to form an image on one side of a recording sheet, on the other side of which an image has already been formed, the recording sheet is guided to a sheet supply means and then conveyed to the recording section again without passing through a two-sided intermediate tray. Further, according to the aforementioned patent application, when the number of recording sheets is one, the recording sheet does not pass through the intermediate tray, and when the number of recording sheets is plural, the recording sheets are once stacked on the intermediate tray and then conveyed to the image forming section again.
In the case where the number of recording sheets is not more than the number of recording sheets which can be accommodated in the sheet conveyance passage in the apparatus, the recording sheets are conveyed without passing through the intermediate tray so as to improve the recording sheet conveyance efficiency.
In the same manner as Japanese Patent Application Open to Public Inspection No. 111955/1983, Japanese Patent Application Open to Public Inspection No. 183471/1987 discloses a copier which includes at least two sheet passages: one is the first sheet passage having no tray, in which a recording sheet on which an image has already been formed, is directly sent to the image forming section and the other is the second sheet passage in which a recording sheet is first stocked on a tray and then sent to the image forming section.
According to the aforementioned patent application, in the case where the number of copies to be made is not more than a predetermined value, the recording sheets are conveyed through the first passage in which they are directly returned to the copy station.
That is, selection can be made between the aforementioned first and second passages according to the number of recording sheets. Further, a predetermined number of recording sheets are conveyed through the aforementioned second passage to the recording section, and other recording sheets are conveyed through the aforementioned first passage.
In the case of the aforementioned conventional copier, there are provided two sheet conveyance passages: one is a sheet conveyance passage in which recording sheets are stacked on the intermediate tray and conveyed to the copy section; and the other is a sheet conveyance passage in which recording sheets are directly conveyed without being stacked on the intermediate tray. Therefore, the following problems are caused.
(1) The structure of the two-sided copier becomes complicated, so that the manufacturing cost is increased.
(2) Changing-over operations of the recording sheet conveyance passage are complicated. Accordingly, mechanical breakdowns are caused.
(3) It is difficult to adjust the timing of sheet conveyance since it is complicated.
(4) Reliability of the apparatus is lowered.
The present invention solves the aforementioned various problems. It is a primary object of the present invention to provide a recording sheet conveyance apparatus for an image forming apparatus characterized in that: in the case of a two-sided copy mode, sheet conveyance and intermediate stacking are smoothly conducted so that recording sheets can be correctly and stably conveyed. As a result, the reliability of recording sheet circulation can be improved, and the conveyance efficiency can be improved. Further, the copying speed can be increased.